1. The Field of the Invention
The present invention relates to high speed optical data transmission systems. More particularly, embodiments of the present invention relate to methods and hardware usable for adjusting assert and de-assert levels in a loss of signal detect circuit within an optical data transmission system.
2. The Relevant Technology
The ever-increasing demand for information communication technologies with faster transmission rates continues to drive the development of new equipment to be utilized with existing high speed data transmission networks. High speed data transmission networks often use optical transceivers and similar devices for transmitting and receiving light carrying digital data over optical fibers. These transceivers can include an optical transmitter, such as a laser, and an optical receiver, such as a photodiode. The transceiver often operates in communication with a host computing system (“host”).
Occasionally, optical transceivers may experience a loss of signal condition in which the received optical power has dropped below levels expected for normal data communication. In order to detect this condition, many optical transceivers are equipped with loss of signal detect circuitry (sometimes referred to as a “signal detect circuitry”). Such a loss in signal in one node of the optical network may be due to, for example, an inoperable optical transmitter on the other node of the network. Also, the optical link between the two nodes may be obstructed or disconnected in some way. Furthermore, the ability of the optical receiver to receive data may have malfunctioned. When a loss of signal occurs, it is important for the associated host (or internally circuitry within the optical transceiver) to be made aware of the loss in signal, since normal operation cannot continue.
Conventional optical transceivers have static loss of signal detect levels which are dependent upon the components set during manufacturing. However, different optical transceivers may have slightly different operational properties in the coupling optics, trans-impedance amplifier and/or photodiode. This slight variation between optical transceivers means that this fixed signal detect level may be detected at different optical receive power levels.
Furthermore, a desirable loss of signal detect level may be different depending on the particular application or communication protocol that the optical transceiver is engaged with. For example, if the communication protocol uses forward error correction, then a lower signal detect level may be tolerable in order to gain the same bit error rate that would be obtainable at higher signal detect levels without forward error correction. Lower bit rate communication protocols may also permit lower signal detect levels, as compared to higher data rate applications.
Accordingly, it would be advantageous to have an optical transceiver loss of signal detector that can be programmed to operate with programmable loss of signal assert levels, which can be changed, set, and/or calibrated depending on the intended use and sensitivity needs existing at the time.